Fungal levels in houses in the Fukushima Daiichi Nuclear Power Plant evacuation zone after the Great East Japan Earthquake

Residences located within 20 km of the damaged Fukushima Daiichi Nuclear Power Plant were evacuated shortly after the Great East Japan Earthquake. The levels of airborne and surface fungi were measured in six houses in the evacuation zone in August 2012 and February 2013. Airborne fungal levels in all of the houses in the summer were higher than the environmental standard levels for residential houses published in Architectural Institute of Japan (>1000 colony-forming units [CFU]/m3). In two houses whose residents rarely returned to visit, fungal levels were extremely high (>52,000 CFU/m3). Although fungal levels in the winter were much lower than those in the summer, they were still higher than environmental standard levels in several houses. Indoor fungal levels were significantly inversely related to the frequency with which residents returned, but they were not correlated with the air exchange rates, temperature, humidity, or radiation levels. Cladosporium spp. and Penicillium spp. were detected in every house. Aspergillus section Circumdati (Aspergillus ochraceus group) was also detected in several houses. These fungi produced ochratoxin A and ochratoxin B, which have nephrotoxic and carcinogenic potential. The present study suggests that further monitoring of fungal levels is necessary in houses in the Fukushima Daiichi Nuclear Power Plant evacuation zone, and that some houses may require fungal disinfection.

Implications: The results suggest that residents’ health could be at risk owing to the high levels of airborne fungi and toxic fungi Aspergillus section Circumdati. Therefore, monitoring and decontamination/disinfection of fungi are strongly recommended before residents are allowed to return permanently to their homes. In addition, returning to home with a certain frequency and adequate ventilation are necessary during similar situations, e.g., when residents cannot stay in their homes for a long period, because fungal levels in houses in the Fukushima Daiichi Nuclear Power Plant evacuation zone were inversely correlated with the frequency with which residents returned to visit their houses.